Tunnel lining grouting is to improve the lining stress conditions and meet the waterproof requirements. The construction gap behind the lining ring is filled with cement and other materials. In the soft soil layer, the part disturbed by the tunnel digging has a weakened stability, and the gap needs to be filled in time to prevent or limit ground subsidence. The actual void value is approximately 130% to 180% of the theoretical void value. Commonly used grouting materials are made of cement, bentonite, fly ash and other additives. The injection pressure is controlled between 10 ~ 30N / cm2, and the filling effect must be guaranteed by a reliable shield tail sealing device. The relationship between the pressing time and the shield advancement can be divided into two types: synchronous pressing and delayed pressing.
1. Prevent surface deformation
The diameter of the shield is larger than the outer diameter of the tunnel lining. When the shield is advanced forward, an annular gap is formed between the lining of the shield tail and the soil layer. After a certain period of time, the soil layer will deform to fill the gap and cause the ground to settle. If the gaps are filled in time with suitable materials, and the stratum is supported, it will not be easy to produce settlement deformation. Therefore, grouting is an effective measure to prevent ground deformation.
2. Reduce the settlement of the tunnel
As mentioned above, the segment emerges from the shield tail, and a gap is created between the segment and the soil, which causes the lower portion of the segment to lose support. Due to the segment’s own weight, sinking occurs, which will affect the original well-looped axis. After the grouting, the segment can lie on the grouting material, as if the tunnel has a cushion layer, which prevents or reduces the settlement of the tunnel, guarantees the quality of the tunnel axis, and meets the engineering requirements.
3.Increase the waterproof performance of lining seams
The tunnel is assembled by prefabricated segments, so there are many longitudinal and circumferential gaps, and these gaps are the weak link of waterproofing. It is envisaged that if a certain thickness of waterproof material is evenly laid on the outer wall of the lining, it will improve the overall The waterproof effect of the tunnel is conceivable, and the grouting is playing this role.
4.Improving the force of the lining
After the grouting, the formation deformation and the formation pressure are prevented, and the slurry is attached to the outer periphery of the lining ring, so that the two are deformed together, thereby improving the stress condition of the lining.
5.Conducive to shield advancement
The effect of the rectifying shield’s advancement and correction has a greater relationship with the relative position of the segments. Sometimes the poor position of the segment restricts the shield’s corrective motion, which is not only unfavorable for the advancement of the effect of correction, but also may damage the segment. If the relative position of the segment and the shield is adjusted by the pressure of the grout, the shield will have an optimal correction condition. If the shield is to be corrected to the right, the grout on the right side can be selected so that the outer periphery of the segment is unilateral. Pressure forces the lining to move to the right, leaning on the left shield tail, and the gap between the inner shield tail and the shield shell on the right side increases, and the shield has more margin to the right. Therefore, the reasonable selection of the grouting position can help the shield to advance and correct the deviation, control the shield’s construction axis, and thereby ensure the overall axis of the tunnel.